Effects of particle exposure and particle-elicited inflammatory cells on mutation in rat alveolar epithelial cells

To investigate mechanisms underlying development of lung adenomas andcarcinomas in rats exposed to poorly soluble particles the relationshipsbetween particle exposure, inflammation and mutagenesis in rat alveolartype II cells were characterized. Rats were exposed to saline or salinesuspensions of 10 and 100 mg/kg of alpha-quartz, carbon black or titaniumdioxide by intratracheal instillation. Fifteen months after exposure,bronchoalveolar lavage (BAL) cells were characterized as to number and typeand lung histopathology performed. The alveolar type II cells were isolatedand cultured in 6 thioguanine (6TG) containing media to select for mutationin the hprt gene. The potential contribution of lung inflammatory cells toin vivo mutagenic responses, were evaluated by co-culturing BAL cells withthe rat alveolar epithelial cell line, RLE-6TN for 24 h and the RLE-6TNcells selected for 6TG resistance. Neutrophilic inflammation was detectedin all rats exposed to 10 and 100 mg/kg of alpha-quartz and carbon blackand 100 mg/kg titanium dioxide; epithelial hyperplasia was observed in ratsexposed to 10 and 100 mg/kg of alpha-quartz and 100 mg/kg carbon black.Hprt mutation frequency was increased in alveolar type II cells from ratsexposed to 10 and 100 mg/kg of alpha-quartz, 100 mg/kg carbon black and 100mg/kg titanium dioxide. In vitro exposure of RLE-6TN cells to BAL cellsfrom rats treated with 10 and 100 mg/kg of alpha- quartz or 100 mg/kgcarbon black increased hprt mutant frequency. Both macrophage andneutrophil enriched BAL cell populations were mutagenic to RLE-6TN cells,however, the mutagenic activity appeared greatest for neutrophils. Additionof catalase to BAL cell:RLE-6TN co-cultures inhibited the increase in hprtmutation frequency. These studies demonstrate exposure of rats to doses ofparticles producing significant neutrophilic inflammation is associatedwith increased mutation in rat alveolar type II cells. The ability ofparticle- elicited macrophages and neutrophils to exert a mutagenic effecton epithelial cells in vitro supports a role for these inflammatory cellsin the in vivo mutagenic effects of particle exposure. The inhibition ofBAL cell-induced mutations by catalase implies a role for cell- derivedoxidants in this response.